Interactions of Light with Organic Chromophores: A Photochemical and Photophysical Investigation
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Abstract
Over the past century, light has emerged as a useful tool finding utility in various fields such as device fabrication, the medical field, as well as utility as an energy source. Chemist have adopted this abundant energy source to do work in material applications and to mediate simple chemical transformations. In regards to the latter, light utilized as a traceless benign reagent for organic transformations has proven fruitful and therefore unequalled in its ability to afford structural complexity from simple starting material(s). Photon absorption of the correct energy elevates organic molecules to a high energy excited state of “short” finite lifetime. In order to afford photoproducts of high selectivity or merely dictate the outcome of a desired photoreaction, control must exist during this short-lived excited state. This dissertation describes a complementary approach to already established photochemical methodologies by which excited state control can be employed in efforts to afford photoproducts of enhanced selectivity. By employing the NEER principle (Non-Equilibrating Excited State Rotamers) and exploiting axial chiral substrates and thereby implementing rotamer control in the excited state, photoproducts of high chemoselectivity, diastereoselectivity and enantioselectivity can be accessed. Additionally, by judicious choice of chromophore control over the excited state process can be gained affording materials of desired physical properties. It was determined that altering the functionality of bio-based feedstocks afforded photoresponsive molecules with altered photoreactivity. Photoacids and photoinitiators were synthesized and their photophysical properties were investigated. Photoinitiators were evaluated for their efficacy towards photochemical polymerization. This dissertation details synthesis, characterization and photophysical investigations of various organic chromophores in efforts to provide mechanistic rationale regarding atropisomeric photoreactions and utility of biobased photoresponsive molecules.